The present invention relates to a method for producing polyphenylene oxides from monohydric phenols, and more particularly it relates to a method wherein monohydric phenols are subjected to oxidation-polycondensation in a reaction vessel with an oxygen-containing gas blown into the vessel in the presence of a complex catalyst of a copper compound and an amine to produce polyphenylene oxides, and in this case, the temperature of gas discharged from a reflux condenser fixed onto the reaction vessel is adjusted to a suitable temperature, whereby the amounts of the amine and water present in the reaction system are adjusted and hence the polymerization reaction can be carried out rapidly and without any fluctuation of reaction time.
The copper-amine complex catalyst promotes an oxidation of a hydrogen atom of a hydroxy group and a hydrogen atom at a para-position in a monohydric phenol molecule to result in a catalytic polycondensation of the monohydric phenol, and this catalytic action is greatly influenced by the proportion of the amounts of a copper compound and an amine forming the complex catalyst.
Further, although the oxidation-polycondensation is indispensable for water formation, an increase of the amount of water formed during the reaction has an adverse influence upon the polymerization to reduce the reaction rate. The respective proportions of the amounts of a copper compound, an amine, water, etc., vary with the progress of the reaction, as mentioned above, and nevertheless, it is required to enhance the reaction rate, i.e. to control the reaction conditions so as to maintain the catalyst activity constantly.
Heretofore, the method of subjecting phenols to the oxidation-polycondensation in the presence of a catalyst of the copper-amine complex to produce polyphenylene oxides has been carried out heeding a solution of phenols dissolved in a solvent, into a polymerization reaction vessel equipped with an agitating element, and vigorously agitating the reaction contents while blowing oxygen or an oxygen-containing gas thereinto. According to the above-mentioned method, since the amine which is a ligand of the complex catalyst escapes outside the reaction system is company with the oxygen-containing gas blown into the reaction system, the amount of the amine in the reaction system is reduced and the proportion of the amounts of copper and amine varies to reduce the catalyst activity.
Thus, in order to overcome such a drawback, various methods have been attempted, such as a method wherein the gas to be discharged outside the reaction system is deeply cooled by a reflux condenser fixed to the polymerization reaction vessel to collect the amine and return it to the reaction system, a method wherein the gas blown in the reaction system in a closed system is used in a circulation manner while oxygen consumed in the reaction is supplemented, to prevent the amine from escaping out of the reaction system, and the like methods. Further, in order to remove water, various methods have been proposed, such as a method wherein anhydrous magnesium sulfate is added to the reaction system in advance to remove the resulting water in the form of water of crystallization, a method wherein the resulting water is adsorbed by molecular sieves to remove it, a method wherein a gas discharged outside the reaction system and containing a solvent, an amine and water is deeply cooled, a condensate is recovered, and then the solvent and the amine obtained by separation of water from the condensate are returned to the reaction system to adjust the amounts of the solvent and the amine in the reaction system, and the like methods.